Module batteries of sodium-sulfur batteries have a large number of cells connected to one another. For example, as disclosed in Patent Literature 1, two or more cells connected in series fond a string, two or more strings connected in parallel form a string group, and two or more string groups are connected in series. The two or more string groups are arranged linearly. The positive electrode current collecting plate is along the inner surface of one side wall, and the positive pole (terminal) penetrates through the one side wall. The negative electrode current collecting plate is along the inner surface of the other side wall, and the negative pole (terminal) penetrates through the other side wall. The one and other side walls face each other.